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Do More Plays = More Injuries?

A few weeks ago, Tommy Lawlor from IgglesBlitz suggested I take a look into whether there is a connection between plays run and injuries. Today, I’ll do that. The theory is relatively straightforward, if you run more plays (for instance, out of a no-huddle offense) you have more opportunities for players to get hurt. Additionally, we can assume that relative levels of fatigue increase with the number of plays. I think it’s also safe to assume that there MAY be a positive connection between fatigue and injury rate.

I guess it’s theoretically possible for fatigue to LIMIT injuries (players aren’t moving as fast or cutting as quickly), but I think it’s more likely to work the other way.

In any case, given Chip Kelly’s state preference for running lots of plays on offense, it’s a worthwhile endeavor to see what, if any, the negative effects will be on the Eagles players.

Methodology

Here’s the tough part. There are A LOT of variables that go into injuries. Additionally, to get a full answer, we’d have to delve very deeply into the plays per game numbers. The ideal way of measuring (as far as I can tell) the correlation would involve logging individual players’ number of plays versus their individual injury occurrences. Unfortunately, I don’t have the data (nor the time/resources) to accomplish such a complete project.

However, I’ve taken a shortcut in an effort to get a quick look at the issue.

From Teamrankings.com, I’ve downloaded the number of offensive plays run for each NFL team from 2008-2012. On the injury side, I’ve used Football Outsiders’ Adjusted Games Lost metric. Note that this statistic is not a straight man-games lost measure. It accounts for the differing injury report designations along with the relative importance of each player (i.e. losing a starting QB is much worse than a 3rd string DE).

While this doesn’t directly address the issue at hand (is injury occurence positively correlated with plays run), it does get at the higher level issue (and perhaps more pertinent question) of how big of an effect will Chip Kelly’s uptempo offense have on the Eagles injury rate.

Note I only went back to 2008 because that’s the earliest season for which I could find the FO AGL stats.

Results

Good news for Eagles fans (at least not bad news); there does not seem to be a connection between Adjusted Games Lost and Offensive Plays run. Here is the chart, the correlation value is -.019. Don’t read into the fact that the correlation is negative; the magnitude suggests there’s no connection either way. UPDATE: I had the X and Y (dependent/independent) flipped in the original chart, now fixed.

As I said, this is by no means a definitive analysis. I’d like a larger sample. It also doesn’t account for TYPE of play, nor does it account for the change in personnel on the field for each play. For example, a kneel down will count as an offensive play despite not carrying any significant risk of injury. Similarly, teams running out the clock with their backups will factor into the data, whereas we are not really concerned with those situations.

Regardless, it’s at least an indication that the Eagles should NOT expect to see a significant increase in rate of injury as they increase the number of plays run. There are a number of potential reasons for this. First of all, the rate of injury is actually very low, so an individual play carries a very small risk. Therefore it should require a relatively large increase in number of plays before we see any effects.

Also, injury rate itself is so variable that we can’t immediately attribute more injuries to more plays. We have to allow for the possibility that increases to overall injury rate are random (though we didn’t see an increase here).

There’s certainly a lot more work that can be done on this subject. There MUST be some correlation, for no other reason than more plays = more opportunities to get hurt. The real question is magnitude, which appears (in this analysis at least), to be very small. We also don’t know whether injury rate is flat or whether it increases as the game progresses (do more injuries occur later in games, perhaps shedding light on the fatigue factor).

For now though, there’s no reason for Eagles fans to worry.

A couple other major takeaways from the data:

– There is a relatively surprising lack of variation in the number of plays run by each team. Over the past 5 seasons, the leader in plays per game has been New England, with 67.9. That makes sense. However, the lowest average belongs to the Buffalo Bills, who ran an average of 59.94 plays per game. Notice the difference between the two teams is just 8 plays per game. As you can imagine, injuries a rare enough that an 8 play increase should not have a major effect on the number of injuries.

– The Eagles averaged 64.64 plays per game over the same timeframe, placing the team 7th overall. Essentially, the Eagles under Andy Reid ALREADY ran more offensive plays per game than most teams.

– The NFL Average from 2008 to 2012 was 63.15 plays per game.

– The highest number of plays run per game in an individual season belongs to last year’s Patriots, who averaged 74.3. The lowest was 56.7 by the 2010 Titans.

6 thoughts on “Do More Plays = More Injuries?”

another complication – if you lose a star player, the starting QB for example, the offenses capabilities are severely diminished, making it more likely that attempted plays will be less successful which in turn makes it more likely that the offense can’t hold the ball and thus runs less plays.
though like you mentioned above, the difference between highest and lowest is so little and at least SOME of those teams must have lost one or more key players so maybe this isn’t much of a factor at all…

like you said… WAY too many variables to get a complete breakdown on this. but excellent work nonetheless.

One reason there may not be much correlation is that a team can only increase the number of plays its offense runs. On defense, they don’t control the tempo. Whereas the injury metric is for more than offense, and includes defense and special teams. So if the Eagles run 75 plays on offense, as opposed to the usual 60 or so, and the other team runs its 60, that takes the total from 120 to 135, or 12.5%, not a huge jump.

This is pretty silly, especially by your very high standards. It is intuitively obvious that more plays will result in more injuries over time and the argument that there really aren’t more plays ducks the initial question.

At a high level, I completely agree with you. Obviously each play run adds an incremental injury risk. However, the bigger question was how will it relate to the Eagles this year, since presumably they will be trying to run a lot more plays. In that respect, I think the post adds some value.

As I said, though, I don’t have the right data to look into the deeper question of how injury rate fluctuates during games. That’s a much more fundamental question for which an answer would be much more valuable. Unfortunately, I can’t currently answer it. In any case, I understand your frustration. I wish I could answer the larger issue as well. (I’m looking for more complete injury data)